The present invention relates to a device and a method for cylinder sensing in an internal combustion engine (also referred to hereinafter as a motor).
In modern motor vehicles, motor management, i.e. control and sensing as well as monitoring of the essential features of the motor, is usually performed by using a control device with a computer.
In particular, ignition and fuel injection must be controlled jointly and adjusted to one another, with the respective operating state of the motor being determined precisely and taken into account in calculating the ignition timing and fuel metering.
An important item of information required by the computer to control ignition and fuel injection involves the position of the crankshaft. Usually a crankshaft sensor is provided to detect the crankshaft position. This crankshaft sensor is for example an inductive sensor that outputs a signal representing the rpm as well as a signal representing at least one selected crankshaft position. As a rule, the selected crankshaft position is top dead center (TDC) for one or more cylinders.
In ignition systems equipped with static high voltage distribution that use individual ignition coils, the computer requires additional information about the position of the camshaft, so that the ignition coil of the cylinder which is at or in the vicinity of TDC in the power stroke can be controlled. Otherwise the ignition coil of the cylinder that is in or in the vicinity of TDC in the exhaust stroke may be undesirably controlled, and caused to fire.
The position of the camshaft is usually detected using a camshaft sensor that delivers a signal when the camshaft is in a position in which a certain cylinder is at TDC in its power stroke for example. This known method is also termed cylinder 1 detection.
By linking the signals from the crankshaft sensor and the camshaft sensor, the ignition times and injection times of all the cylinders can be calculated unambiguously by the computer.
The method according to the prior art mentioned above has the disadvantage that two expensive sensors and correspondingly expensive wiring are required.
Accordingly, it is an object of the present invention to provide a device and a method for cylinder sensing in an internal combustion engine without requiring an additional camshaft sensor.
This object is achieved by a device for cylinder sensing in an internal combustion engine with a crankshaft sensor device to detect a crank angle and a predetermined crankshaft position and to output corresponding crankshaft signals; an ignition device for igniting the respective cylinders of the internal combustion engine by generating corresponding high voltage pulses in response to appropriate control signals; and a control device for receiving the crankshaft signals and outputting the control signals to the ignition device as a function of at least the crankshaft signals. The control device is designed such that, while receiving a crankshaft signal corresponding to a predetermined crankshaft position during a cylinder sensing phase, it outputs a control signal to generate a high-voltage pulse with a predetermined amplitude that can be reached in at least one specific cylinder; an ignition detection device to detect whether and/or at which ignition voltage the specific cylinder has been ignited by the high-voltage pulse, and output a corresponding ignition detection signal; and a cylinder sensing device to determine whether the specific cylinder in the predetermined crankshaft position is in its power stroke, based on at least the ignition detection signal.
This object as achieved by a method for cylinder sensing in an internal combustion engine with the following steps: detecting the crank angle and a predetermined crankshaft position and outputing corresponding crankshaft signals; generate a high-voltage pulse with a predetermined amplitude that can be reached in at least one specific cylinder when a predetermined crankshaft position is detected during a cylinder sensing phase; detecting whether and/or at what ignition voltage the specific cylinder has been ignited by the high-voltage pulse and output a corresponding ignition detection signal; and determining whether the specific cylinder is in the predetermined crankshaft position in its power stroke, based on at least the ignition detection signal.
The principle of the present invention is based on the fact that the ignition voltage at a predetermined crankshaft position, which is at or in the vicinity of TDC in the cylinder in question, depends on, among other things, the pressure prevailing in the cylinder. Thus the ignition voltage at 1 bar is typically 5 kV, while at approximately 5-7 bar it is typically about 13-20 kV. These pressures and ignition voltages can become established in two different cylinders of a motor when one cylinder is at or in the vicinity of TDC in its exhaust stroke (valves open) and the other cylinder is at or in the vicinity of TDC in its power stroke (valves closed).
In addition, by detecting the different ignition voltages, a determination can be made as to which of the cylinders is in the power stroke, so that the ignition sequence can be determined without requiring a conventional camshaft sensor.
For purposes of detection, in particular there is the first possibility that the high-voltage pulse supplied during the cylinder sensing phase is a normal high-voltage pulse, in other words, a high-voltage pulse whose amplitude can reach a typical value of approximately 13 kV required for ignition during the power stroke. In this case, the actual ignition voltage is detected and the result evaluated for cylinder sensing.
Secondly, the high-voltage pulse supplied during the cylinder sensing phase can be a reduced high-voltage pulse, i.e. a high-voltage pulse whose amplitude cannot reach the value of typically about 13 kV required for ignition during the power stroke, but only a value that is typically 7 kV and is sufficient for ignition during the exhaust stroke. In this case a determination is made as to whether a spark has actually occurred and the result is evaluated for cylinder sensing.
Once the initial sequence of the cylinders has been determined, all the subsequent ignition times until the motor next stops can be determined by sensing the crankshaft position using the crankshaft sensor. In other words, the cylinder sensing process needs only be performed during the starting phase of the motor. Therefore the fact that the usual camshaft sensor can be eliminated is an especially advantageous feature of the present invention.
According to a preferred embodiment, the predetermined crankshaft position is top dead center for the specific cylinder. This offers the advantage that the pressure differential between the power stroke and the exhaust stroke and hence the reliability of the measurement is greatest in this crankshaft position.
According to an additional preferred improvement according to claim 4, the predetermined amplitude is smaller than the amplitude required for ignition during the power stroke. This offers the advantage that no additional control expense for setting the value of the amplitude of the high-voltage pulse is required. In this case the ignition detection device is preferably so designed that it detects the ignition voltage of a specific cylinder. The ignition detection signal is then either the detected ignition voltage itself or a signal that can be derived from it unambiguously.
According to another preferred embodiment, the cylinder sensing device has a storage device for storing at least one ignition reference signal and a comparison device for comparing the ignition detection signal with the ignition reference signal. The ignition reference signal is preferably a reference voltage value chosen so that it is smaller than the voltage amplitude required for ignition when the cylinder in question is in the power stroke, but higher than the voltage amplitude required for ignition when this cylinder is in the exhaust stroke. The ignition reference signal for example can be 9 kV. This improvement is easy to implement but assumes that the voltage required for ignition is sufficiently different in the compressed and noncompressed states in order to permit reliable cylinder sensing.
According to still another preferred embodiment, a plurality of ignition reference signals from correspondingly different operating states of the internal combustion engine is stored in the storage device and the comparison device is so designed that it uses an ignition reference signal corresponding to the current operating state of the internal combustion engine for comparison. With such a design, consideration can be given to the fact that the ignition reference signal depends on the operating state of the motor. The term "operating state" therefore also subsumes internal parameters such as compression pressure as well as external parameters including the external temperature or air pressure.
In a further preferred embodiment, the cylinder detection device is so designed that it detects the ignition voltage of the specific cylinder during two successive periods of the AC ignition voltage. In this case the cylinder sensing device preferably has a storage device for storing the first ignition detection signal and a comparison device for comparing the first ignition detection signal with the second ignition detection signal. If the first ignition detection signal represents a higher ignition voltage, the specific cylinder is in the power stroke during the first revolution, otherwise during the second revolution.
In a further preferred embodiment, the ignition detection device is so designed that it detects the ignition voltage of at least two specific cylinders corresponding to one another during the same period of the AC ignition voltage. In this case the cylinder sensing device preferably has a comparison device for comparing the ignition detection signals corresponding to two specific cylinders. The simultaneous application of the ignition voltage to the two specific cylinders and the subsequent comparison of the detection signals has the advantage that the other influential parameters that affect ignition voltage, such as electrode spacing, gas composition, and gas dynamics for example, are as a rule the same in both cylinders and therefore compensate one another.
In another preferred embodiment, the predetermined amplitude, in other words the ignition reference signal, is smaller than the amplitude required for ignition during the power stroke.
Such a reduced amplitude can be achieved for example by reducing the energy supplied on the primary side to the ignition coil, specifically the primary current, or by reducing the steepness of the shutoff flank of the primary current.
In this case, the predetermined amplitude, in other words the ignition reference signal, is preferably higher than the amplitude required for ignition during the exhaust stroke.
In another preferred embodiment, the ignition detection device is preferably designed to determine whether the specific cylinder has been ignited, in other words it performs a YES/NO determination.
Preferably, the ignition device is designed to generate bipolar high-voltage pulses. In addition to the improvements listed above which are preferably made in a unipolar ignition device, there are additional advantageous possibilities for cylinder sensing with such a bipolar ignition device.
In another preferred embodiment the control device is designed to output a control signal for generating a bipolar high-voltage pulse with a different first and second predetermined amplitude as a function of the respective half-waves. In other words, in this improvement, the positive and negative half-waves of the ignition voltage have different values.
Preferably in this case the second predetermined amplitude is the amplitude required for ignition during the power stroke, and the first predetermined amplitude is smaller than the second predetermined amplitude and higher than the amplitude required for ignition during the exhaust stroke. In this case it is likewise possible to design the control device so that it increases the first predetermined amplitude during subsequent periods of the AC voltage to ignite a spark until the predetermined amplitude is higher than the amplitude required for ignition during the exhaust stroke.
According to another preferred embodiment, the ignition detection device is designed to determine whether the specific cylinder has been ignited during the first and/or second half-wave. If the specific cylinder has already been ignited in the first half-wave, it is in the exhaust stroke; otherwise it is in the power stroke.
Preferably the ignition detection device is located on the primary winding of the respective ignition coil. The advantage of this design is that it is readily possible to detect the time of appearance of an ignition spark in the primary igntion coil and to obtain from this the desired information about the pressure ratios in specific cylinders or their current cycles.
Advantageously, a start-signal generating device for generating a start signal when starting the internal combustion engine and outputting the start signal to the control device to determine the cylinder sensing phase is provided. This is advantageous since, as already mentioned above, cylinder sensing is required only at the beginning of operation of the motor. For example, the starting signal can be output with the ignition key in the starting position.
In the following the present invention will be explained in greater detail in conjunction with preferred embodiments and referring to the accompanying drawings.